Our study is directed towards understanding the interactions that exist among the proteins that constitute the RNA polymerase portal of the cystoviruses. This molecular machine selects, packages, and replicates the viral RNA genome segments. One portal is located on each vertex of the 12-sided polymerase complex (PX) a structure that forms the viral core. This bacteriophage family constitutes a unique bacterial reovirus that serves as a simple and important molecular model for their clinically significant cousins, the Reoviridae. Our overall objective is to establish a detailed structural model for the reoviruses portal apparatus using cryo-electron microscopy (cryo-EM). We will then better understand how they replicate and package their double-stranded RNA (dsRNA) genomes. This knowledge is of critical importance in the design of antiviral pharmaceuticals for pathogenic reoviruses, in particular rotavirus, a significant cause of childhood morbidity in third world countries. My developmental and career objective is to employ a qualified research team that studies the molecular biology and structure of clinically significant viruses at the City College of New York (CCNY) Medical School. The cystovirus model offers an excellent introductory virus project that utilizes the resources for molecular and structural biology recently established at the CCNY campus in particular the New York State Foundation for Science, Technology and Innovation (NYSTAR) funded New York Structural Biology Center (NYSBC). The Gottlieb laboratory personnel have utilized the hardware and software at this new facility and have published the center's first electron-cryo- tomography paper. We are completing a second electron cryo-microscopy paper that constitutes the preliminary study for this proposal. We have recently established a new optical method to examine the dynamic conformational shape changes that occur in viral proteins during the infection process. This research is performed in collaboration with physicists at the Institute for Ultrafast Spectroscopy and Lasers (IUSL) on the CCNY campus. We have included an aim in the research plan directed towards perfecting our optical assays for the analysis of biochemically active cystovirus PX. The PX is known to radically expand during viral RNA packaging and replication. We believe that this portion of our research proposal fits well within the goals of the current project. We anticipate that the optical qualities of viral proteins that we discover are applicable to human pathogens, in particular influenza.